1. Field of the Invention
The present invention relates to pneumatic averaging devices for averaging two or more input pressure signals while permitting the input pressure signals to also be utilized separately.
2. Prior Art
In the prior art, air data probes have been advanced which rely upon determining the differential between pressures at ports on a hemispherical head for determining the angle of attack or angle of sideslip of an aircraft. One such device is shown in U.S. Pat. No. 3,318,146, which describes the basic equations for determining angle of attack, angle of sideslip, Mach number and other air data parameters from a hemispherical head probe which has five pressure ports at the forward or leading end. U.S. Pat. No. 3,364,742 shows an air data sensing probe having orifice restrictors in each of two instrument lines leading from an input chamber. The restrictors are used to permit a single probe to operate dual systems or instruments.
Additionally, static sensing probes which provide for an average or normalized static pressure wherein the static pressure is sensed at two different ports plumbed into a single outlet are illustrated in U.S. Pat. Nos. 3,482,445, 3,585,859 and 4,096,744. All these patents also include surface contouring for providing a desired pressure profile along the probe itself for pressure compensation. In each instance rather than providing for an average pressure difference output between two of the sensing ports, and also providing for signals indicating the pressure at the two inputs that are averaged, only the average or normalized pressure is provided for use. U.S. Pat. No. 4,096,744 (FIG. 9) also illustrates the averaging of right and left sensor outputs by manifolding from sensors on opposite sides of an aircraft fuselage.
In the computation of angle of attack ratio derived from a hemisphere-cylinder flow angle sensor, such as that shown in U.S. Pat. No. 3,318,146, equations in the patent and also those described on Page 3 of Bulletin 1014 (copyright 1974) of Rosemount Inc., the owner of U.S. Pat. No. 3,318,146 indicate that for angle of attack and sideslip utilizing a five hole sensing probe, the pressure designated "p.sub.4 " can be derived from pneumatic pressure averaging (which is merely manifolding the two pressures together) within the sensor itself. It should be noted that when both angles of attack and sideslip are desired from a single sensor, it is necessary to compute. These equations are described on Page 3 of the bulletin and in the patent. A study of these equations will indicate that if a single failure is experienced in the pressures utilized for the differential pressure measurements or in the computation circuitry that is utilized, there would be a failure in both the ratio determinations for angle of attack and angle of sideslip.
A common transducer configuration made by Rosemount Inc. for aircraft mounting is a two sensor air data module made specifically for calculating angle of attack or angle of sideslip where the pneumatic average of two of the ports, designated p.sub.4, is obtained. In a typical application, it has now become desirable to measure both the angle of attack and angle of sideslip using two transducer air data modules. For this application the average pressure p.sub.4 between two of the ports on the hemispherical head is necessary as well as the individual pressures that are averaged. As herein shown, two air data modules, each with two pressure sensors, can be utilized to compute angle of attack, and angle of sideslip and each system is then completely independent rather than cross coupled. The present invention provides for redundancy in operation.